Survival Kinetics of HeLa S-3 Cells after Incorporation of3H-thymidine or3H-uridine

Abstract

The survival kinetics of mammalian tissue-culture cells containing tritium-labelled nuclebsides have been studied. He La S-3 cells were allowed to incorporate various amounts of H3-thymidine or H3-uridine into their DNA or RNA. Due to the short mean free path of the tritium-decay [beta]-ray, incorporation of H3 -thymidine irradiates mainly the nucleus, while most of the radiation from the H3 -uridine is absorbed by the cytoplasm. A model which takes into account the persistence of [beta]-radiation from the labelled nucleic acids and the dose-rate reduction due to cell-division was constructed for the expected survival kinetics. The experimental data were fitted to this model by means of a digital computer. It was found that the "hit number" was not significantly different from the values previously reported for x-rays. It was concluded that all the cell-killing seen can be accounted for by the [beta]-radiation to which the cell is exposed.